Described below is a device for separating ferromagnetic particles from a suspension, using a tubular reactor through which the suspension can flow and which has at least one magnet.
In order to extract ferromagnetic components which are contained in ores, the ore is ground into a powder and the powder obtained is mixed with water. A magnetic field generated by one or more magnets is applied to this suspension, as a result of which the ferromagnetic particles are attracted so that they can be separated from the suspension.
DE 27 11 16 A discloses a device for separating ferromagnetic particles from a suspension, in which a drum consisting of iron rods is used. The iron rods are alternately magnetized during the rotation of the drum, so that the ferromagnetic particles adhere to the iron rods while other components of the suspension fall down between the iron rods.
DE 26 51 137 A1 discloses a device for separating magnetic particles from an ore material, in which the suspension is fed through a tube which is surrounded by a magnetic coil. The ferromagnetic particles accumulate at the edge of the tube, while other particles are separated through a central tube which is located inside the tube.
A magnetic separator is described in U.S. Pat. No. 4,921,597 B. The magnetic separator includes a drum, on which a multiplicity of magnets are arranged. The drum is rotated oppositely to the flow direction of the suspension, so that ferromagnetic particles adhere to the drum and are separated from the suspension.
A method for the continuous magnetic separation of suspensions is known from WO 02/07889 A2. This uses a rotatable drum in which a permanent magnet is fastened, in order to separate ferromagnetic particles from the suspension.
In known devices, a tubular reactor, through which the suspension flows, is used to separate the ferromagnetic particles from the suspension. One or more magnets, which attract the ferromagnetic particles contained in it, are arranged on the outer wall of the reactor. Under the effect of the magnetic field generated by the magnets, the ferromagnetic particles migrate onto the reactor wall and are held by the magnet arranged on the outside of the reactor.
FIG. 1 shows the profile of the force of attraction as a function of the radial position in a known device. The distance from the middle of the reactor is plotted on the horizontal axis, the dot and dash line corresponding to the midline of the reactor. The force of attraction is plotted on the vertical axis. The force of attraction, which is proportional to the magnetic field gradient, has a parabolic profile, is minimal at the center of the reactor and maximal on the inner wall of the reactor. Accordingly, particles which are located in the middle of the reactor are not attracted, or only partially attracted, by the magnet or magnets and subsequently separated from the suspension. In particular with high speeds, this effect means that a considerable part of the suspension flowing through the reactor is not attracted to the inner wall of the reactor, and leaves the reactor again without the ferromagnetic particles being separated. For this reason, the separation ratio in known devices is unsatisfactory with significant flow rates.